Title: The nuclear spin coherence and the spin Hall effect in semiconductors
Speaker: Prof. Yuzo Ohno（Research Institute of Electrical Communication, Japan）
Time: 10:30(AM), May 21, 2010
Venue: Academic Salon, Institute of Semiconductors, CAS
Abstract: In this Forum, I will present our studies on (1) the nuclear spin coherence in GaAs/AlGaAs quantum wells and (2) the carrier concentration dependence of the spin Hall effect in n-GaAs.
(1) A new class of nuclear magnetic resonance (NMR) with high-sensitivity and high-spatial resolution has become important tool to investigate intriguing spin-related physics in semiconductor nanostructures, in which one can control the interaction between electron and nuclear spins by electrical and optical means. In this talk, we demonstrate manipulation of nuclear spin coherence in a GaAs/AlGaAs quantum well by optically-detected nuclear magnetic resonance (NMR). Phase shift of the Larmor precession of photoexcited electron spins is detected to read out the hyperfine-coupled nuclear spin polarization. Multi pulse NMR sequences are generated to control the population and examine the phase coherence in quadrupolar-split spin-3/2 75As nuclei. The phase coherence among the multi-level nuclear spin states is addressed by application of pulse sequences that are used in quantum gate operations. (2) We investigated doping concentration (ND) dependence of the extrinsic spin Hall effect (SHE) in n-doped GaAs with ND raging from 3 ′ 1016 cm-3 to 5 ′ 1017 cm-3. By using scanning Kerr microscopy (SKM) measurement, we observed the Kerr rotation signal due to the spin accumulation near the channel edges in all the samples with different ND. Moreover, the position and in-plane magnetic field dependence of the Kerr rotation signal are found to vary with ND. We analyzed the ND dependence of the spin Hall conductivity by taking account of the ND-dependent spin lifetime based on the typical drift-diffusion model.
About speaker：
Associate Professor Yuzo Ohno received Ph. D. degree from the University of Tokyo in 1996. He joined Professor Hideo Ohno’s group at Research Institute of Electrical Communication, Tohoku University as a Research Associate (1996) and then as an Associate Professor (2001~). He received the JSPS Prize (2005), Sir Martin Wood Prize (2006), and Marubun Prize (2008). He is a member of JSAP, JPS, and APS. Since 1996, he worked together with Professor Hideo Ohno and Associate Professor Fumihiro Matsukura in Tohoku University, and succeeded in demonstration of electrical spin injection (in collaboration with University of California, Santa Barbara), and electric field control of ferromagnetism. They have also been investigating coherent spin dynamics in nonmagnetic semiconductor quantum structures by time-resolved optical pump and probe method. They demonstrated long spin lifetime of electrons in GaAs/AlGaAs quantum wells grown on (110) plane, and successfully demonstrated the all optical nuclear magnetic resonance (in collaboration with University of California, Santa Barbara), gate-control of dynamic nuclear polarisation, and optical detection of coherence of nuclear spins based on high-sensitivity time-resolved Kerr/Faraday rotation techniques.